DP Slave Missing

H.SAPER

Hello,

Dear Sirs, My system was work properly, suddenly two slaves missing Slave3 and Slave4, I have changed DP plugs and I have checked the profibus cable also was Ok.

So, first how I can check if DP port on the PLC CPU is work properly or not?

secondly, How I can jump one of slaves? i.e I'm going to power off 4th slaves because the unit 4 some times we do not use it.

attached illustrate what S7 CPUs I'm using 

Regards.

 Hello Hassan;

After running well for years, a Profibus network can start failing simply due to aging of components and attached equipment. Sometimes it is a long process to determine the unique cause of a failure.

For example, prolonged vibrations can over time slacken the screw connections inside a Profibus connector, loosening the contacts with each wire in the cable, and especially the quality of connection with the shield. So when verifying a connector re-attach all wiring inside it as if this is a new installation. In case of doubt, change connectors for new ones. 

A minimum test for the cable can be a continuity test between the nodes, making sure that the red wire is continuous and presents no short- or open circuit over the segment. Same tests should be applied to the green wire and the shield. This a test that could require a Profibus tester, it can locate issues on the installed cables that are difficult to diagnose with simple multimeters. If you do not have acces to one, from Procentec, SMAR, Softing... call in an integrator who masters this type of equipment to do the tests

One very important test on a Profibus network is the termination circuit, which must be ON at each end-node (in your sketch, the CPU and Slave 4) and these nodes must remain powered at all times. If you plan to remove power to slave 4 (as you mentioned earlier), either turn ON the terminator switch on slave 3 before you do so, or install an active terminator (powered by its own 24 VDC un the field) to maintain the network stable.

Active bus terminators part number is: 6ES7 972-0DA00-0AA0)

Instructions for the permanent termination of a bus segment

https://support.industry.siemens.com/cs/us/en/view/2157453

Removing the power from a node will cause error messages on the network and fault LEDs on the CPU. To block these you should use SFC 12, D_ACT_DP, in your program:

Enabling a disabled DP slave with SFC 12 "D_ACT_DP"

https://support.industry.siemens.com/cs/us/en/view/19730984

Hope this helps,

Daniel Chartier